The present application claims priority to Japanese patent application of Tanabe et al., filed Mar. 23, 2000, No. 2000-081908, and Japanese patent application of Tanabe et al., filed Mar. 30, 2000, No. 2000-094708.
1. Field of the Invention
The invention relates to an airbag for use in a head protective airbag device mounted on a roof-side rail section of a motor car, an airbag device for lateral collision and mounted on a seat, and the like.
2. Description of Related Art
Conventionally, for example, with a head protective airbag device, an airbag is folded and received to extend over a door and a peripheral edge of an opening on windows on a vehicle-interior side. When an expansion gas inflows, the airbag is developed and expanded in a manner to cover the opening. The airbag is provided with an expansion section, which allows an expansion gas to inflow to thereby expand in a manner to separate a vehicle-interior side wall and a vehicle-exterior side wall from each other.
A plurality of linear connections are arranged in a region of the expansion section (see Japanese Patent Laid-Open No. 321535/1999). The linear connections join opposite portions of peripheral walls, which constitute the expansion section, to one another in a linear fashion. Such linear connections are arranged in order to make peripheral edges and a central portion of the expansion section substantially uniform in thickness. Further, with a head protective airbag device, the linear connections are arranged to make an airbag exert tensile forces in a longitudinal direction to prevent the airbag from moving outside the vehicle even when the airbag is subjected to pushing forces toward the outside of the vehicle.
However, if end portions of the linear connections are small in area, stress concentration is liable to occur on the end portions of-the linear connections at the time of expansion of the expansion section. Thus if the end portions are small in area, peripheral walls, which constitute the expansion section in the vicinity of the end portions, are in some cases broken.
Therefore, the linear connections including the end portions are arranged in a wide dimension.
However, if all the linear connections including the end portions are arranged in a wide dimension, a volume of the expansion section, into which an expansion gas is caused to flow, and an expansion area decrease. That is, when the linear connections are formed to be wide, the cushioning quality of an airbag is influenced thereby.
There is a need to solve the above-mentioned problems and to provide an airbag capable of arranging linear connections without causing breakage of peripheral walls at the time of development and expansion, while holding down reduction of a volume and an expansion area.
Accordingly, an embodiment of the present invention provides an airbag comprising an expansion part permitting an expansion gas to inflow to expand a peripheral wall, and linear joining portions arranged in a region of the expansion part and constituted by joining facing portions of the peripheral wall in a linear manner. The linear joining portions comprise a base, curved portions and swelling portions. The base is arranged to be substantially linear. Each of the curved portions is connected to a respective base and curvilinearly extends from the respective base thereof. The swelling portions are arranged at tip ends of the curved portions to smoothly connect outer peripheral edges thereof to outer peripheral edges of the curved portions. And the linear joining portions are arranged in accordance with B0 less than R2 less than R1 is established where B0 is a widthwise dimension near portions of the base connected to the curved portions, R1 is a radius of curvature of the outer peripheral edges of the curved portions, and R2 is a radius of curvature of the outer peripheral edges of the swelling portions.
With the airbag according to the invention, end portions of the linear joining portions are formed in a manner to be made contiguous to the swelling portions through the curved portions from the substantially straight base. And the swelling portions connect outer peripheral edges thereof smoothly to the outer peripheral edges of the curved portions, and the outer peripheral edges of the swelling portions have a radius R2 of curvature greater than a width dimension BO of the base. Therefore, stress concentration is reduced around the swelling portions when the expansion portions expand.
Also, the outer peripheral edges of the curved portions have a radius R1 of curvature larger than the radius R2 of curvature of the outer peripheral edges of the swelling portions. Therefore, stress concentration is reduced around the curved portions.
At the end portions of the linear joining portions, the swelling portions are made wide. However, inner peripheral edges of the curved portions, which connect the base and the swelling portions, are recessed to enable making small the curved portions and the base. Therefore, reduction in volume of the expansion portions can be held down as much as possible.
Accordingly, with the airbag according to the invention, the linear joining portions can be arranged without causing breakage of the peripheral wall at the time of development and expansion and with reduction in volume and expansion area held down as much as possible.
And it is desired that the portions of the base near the curved portions are arranged substantially in parallel to a main flow of the inflowing expansion gas, and the swelling portions are arranged offset from the base in directions substantially perpendicular to the main flow of the expansion gas.
With such constitution, the swelling portions do not directly interfere with a main flow of an expansion gas, and stress concentration can be reduced around the swelling portions. Therefore, it becomes possible to reduce an area of the linear joining portions as well as an area of the swelling portions on the end portions. And it becomes possible to further increase a volume and expansion area of the airbag.
Also, the swelling portions may be arranged offset from the base toward branching flow passages branching from the main flow passage, through which the main flow of the expansion gas flows.
With such constitution, the swelling portions do not further interfere with a main flow of an expansion gas, and stress concentration can be reduced around the swelling portions. Therefore, in this case, it becomes possible to reduce an area of the linear joining portions as well as an area of the swelling portions on the end portions. That is, it becomes possible to increase a volume and expansion area of the airbag.
Further, in the case where the airbag is formed by hollow-weaving, it is desired that a radius of curvature R1 of the outer peripheral edges of the curved portions is in the range of 15 to 100 mm, and a radius of curvature R2 of the outer peripheral edges of the swelling portions is in the range of 10 to 15 mm.
With an airbag constituted in such manner, the linear joining portions can be arranged with reduction in volume and expansion area held down as much as possible.
Incidentally, the radius R1 of curvature of the outer peripheral edges of the curved portions are below 15 mm, stress concentration is liable to occur around the curved portions at the time of expansion of the expansion part to cause the possibility of breakage of the peripheral wall at the time of expansion and development of the airbag. Also, when the radius R1 of curvature exceeds 100 mm, the degree of bending from the base decreases, so that the main flow of the expansion gas becomes liable to interfere with the swelling portions. And it is not preferable to lengthen the curved portions so as to avoid this, since the airbag is made small in volume and expansion area.
Also, the radius R2 of curvature of the outer peripheral edges of the swelling portions are below 10 mm, stress concentration is liable to occur around the swelling portions at the time of expansion of the expansion part to cause the possibility of breakage of the peripheral wall at the time of expansion and development of the airbag. Also, when the radius R2 of curvature exceeds 15 mm, stress concentration is reduced therearound. However, this is not preferable since the airbag is made small in volume and expansion area.
And in the case where there is a need of partially making the airbag compact when the airbag formed in hollow-weaving is to be folded for storage, the airbag may be constituted according to a second embodiment in the following manner.
More specifically, an airbag according to the second embodiment is folded and received in a peripheral edge of an opening on a vehicle-interior side and a body side and is developed and expanded in a manner to cover the opening when an expansion gas inflows. Also, the airbag comprises an expansion part and a thin-walled non-expansion part. The expansion part is constituted to comprise a vehicle-interior side wall portion and a vehicle-exterior side wall portion, and expands in a manner to separate the vehicle-interior side wall portion and the vehicle-exterior side wall portion from each other when the expansion gas is made to inflow. The thin-walled non-expansion part is made thinner than a sum of thicknesswise dimensions of the vehicle-interior side wall portion and the vehicle-exterior side wall portion to inhibit inflowing of the expansion gas. And the thin-walled non-expansion part together with the expansion part is formed into a bag shape by hollow-weaving with a portion of a bag-shaped peripheral wall cut off.
With the airbag according to the second embodiment, when the airbag is woven by hollow-weaving, the thin-walled non-expansion part together with the expansion part is formed in a bag-shape. Portions of the peripheral edge on the woven portion, which constitutes the thin-walled non-expansion part, are cut off to enable forming the thin-walled non-expansion part.
Incidentally, with the prior art, an airbag is manufactured by hollow-weaving, and a cloth material for a thin-walled non-expansion part is separately cut into a predetermined shape. And the cloth material for a thin-walled non-expansion part is joined to an airbag to manufacture the same (Japanese Patent Laid-Open No. 6749/2000). Therefore, such prior art airbag takes time in manufacture and involves an increase in manhour for manufacture and cost. In addition, the reason for formation of the thin-walled non-expansion part is to enable preventing the thin-walled non-expansion part from becoming bulky and interfering with a room lamp and an air-conditioning duct disposed about a peripheral edge of an opening when the airbag is to be folded.
With the airbag according to the second embodiment, however, only the cutting-off operation after hollow-weaving makes it possible to form a thin-walled non-expansion part to simply manufacture an airbag.
Accordingly, even when provided with a thin-walled non-expansion part made thin in thickness, the airbag according to the second embodiment can be easily manufactured to be reduced in manhour for manufacture and cost.
With the above-mentioned airbag, it is desired that a thin-walled non-expansion part is constituted by a vehicle-interior side portion on a peripheral edge when the airbag is formed by hollow-weaving. This is because an cut off end portion on the thin-walled non-expansion part can be prevented from being exposed to a vehicle-exterior side at the time of development and expansion of the airbag. Therefore, it is possible to make feeling favorable even when an occupant contacts with the thin-walled non-expansion part.
It is desired that a method of manufacturing the airbag according to the second embodiment be as follows.
First, an airbag stock configured to comprise a product shape of the airbag and a cut-off hem on a peripheral edge of the product shape is woven by hollow-weaving. Also, at the time of hollow-weaving, a spare bag-shaped portion, which is communicated to a woven portion of the thin-walled non-expansion part, is woven on the cut-off hem.
Then, at the time of cutting-off of the cut-off hem, the spare bag-shaped portion is cut off to form an opening on the woven portion of the thin-walled non-expansion part.
Thereafter a cutting jig is inserted into the woven portion of the thin-walled non-expansion part from the formed opening to cut off a portion of the peripheral wall, thus enabling manufacturing an airbag.
With the above-mentioned method, at the time of hollow-weaving, a spare bag-shaped portion, which is communicated to a woven portion of the thin-walled non-expansion part, is woven on the cut-off hem. Therefore, at the time of cutting-off of the cut-off hem, the spare bag-shaped portion is cut off to form an opening on the woven portion of the thin-walled non-expansion part. And a cutting jig can be inserted into the woven portion of the thin-walled non-expansion part from the opening to cut off a portion of the peripheral wall on the woven portion of the thin-walled non-expansion part.
Accordingly, the manufacturing method of the present invention makes it possible to more simply form thin-walled non-expansion part.
Other features and characteristics of the present invention, as well as the methods of operation of the invention and the function and interrelation of the elements of structure, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this disclosure.